Collaborative Research: Molecular Growth in Time-varying, Non-premixed Flames

这是一项协调的、全面的分子生长化学研究，涉及耶鲁大学和乔治华盛顿大学的团队参与的强迫、时变火焰中。使用一套基于激光的技术来确定主要组分浓度、小分子自由基浓度、速度和温度。较大的物种使用与质谱仪耦合的新型脉冲微探头进行采样。实验工作得到了火焰结构的时间相关计算的补充，其中包括分子生长化学。研究了三种时变的非预混火焰：不发光的氮气稀释甲烷火焰，微弱发光的40%乙烯-60%氮气火焰，以及更亮的60%乙烯-40%氮气火焰。第一个火焰将为该方法提供一个基本情况和示范环境。观察到稳定的“40/60”火焰沿中心线具有最高的烟尘负荷，而“60/40”火焰在边缘附近显示出最高的烟尘水平，这表明分子生长化学和一包流体经历的时间-温度历史之间存在微妙的相互作用。其目的是为竞争烟尘增长模型的严格测试提供实验数据，并指导人们对这一过程的直观理解。对燃料热解和分子生长化学形成的大量中间碳氢化合物的浓度进行了时间分辨测量；这些四维数据与高保真的温度和速度场相结合，以实验方式绘制出整个粒子初始过程；分子生长化学使用现有的三个最进化的烟尘形成化学模型进行了数值模拟。广泛的影响陆源燃烧产生的烟尘颗粒现在被公认为构成重大的健康风险，并已成为严格的新EPA法规的主题。从发动机设计师的角度来看，对烟尘的担忧超出了这些监管问题的范畴。燃烧室主要区域的高烟尘浓度导致燃烧室衬里的高热辐射负荷。衬里表面的烟尘涂层将显著提高底层金属温度。新燃烧器运行时的高压加剧了这些问题，因为烟尘的产生对压力非常敏感。如果要控制烟尘和与之相关的问题，以实验测量支持的计算模型的形式定量了解烟尘生长和氧化机制是必不可少的。拟议工作的一个重要组成部分将是对本科生和研究生进行化学和机械工程方面的教育。此外，正在进行的K-12教育活动将继续进行，并通过教师研究经验(RET)计划得到扩大。

This is a coordinated, comprehensive study of molecular growth chemistry in forced, time-varying flames involving groups at Yale and George Washington University. Major species concentrations, small radical concentrations, velocity, and temperature are determined using a suite of laser-based techniques. Larger species are sampled using a novel pulsed microprobe coupled to a mass spectrometer. The experimental work is complemented by time-dependent computations of flame structure that include molecular growth chemistry. Three time-varying, non-premixed flames are studied: a non-luminous, nitrogen-diluted methane flame, a40% ethylene-60% nitrogen flame that is slightly luminous, and a 60% ethylene-40% nitrogen flame that is more luminous. The first flame will provide a base case and demonstration environment for the approach. The steady "40/60" flame has been observed to have peak soot loadings along the centerline while the "60/40" flame shows highest soot levels near the edges, indicative of the subtle interplay between molecular growth chemistry and the time-temperature history experienced by a packet of fluid. The goal is to provide experimental data for a rigorous test of competing soot growth models, and also to guide the development of intuitive understanding of the process. Time resolved measurements of the concentrations are made for a host of intermediate hydrocarbons formed from fuel pyrolysis and molecular growth chemistry; these four-dimensional data are combined with high-fidelity temperature and velocity fields to map experimentally the entire particle-inception process; and molecular growth chemistry is simulated numerically using three of the most evolved soot-formation chemistry models available.Broader impactsCombustion-generated soot particulates from land-based sources are now acknowledged to pose a significant health risk and have been the subject of stringent new EPA regulations. From the standpoint of an engine designer, the concern about soot goes beyond these regulatory issues. High soot concentrations in combustor primary zones contribute to high thermal radiation loads on combustor liners. Soot coatings on liner surfaces will drastically increase underlying metal temperatures. These issues are exacerbated by the high pressures at which new combustors are operated, because soot production is very sensitive to the pressure. If soot and the problems associated with it are to be controlled, quantitative understanding of the soot growth and oxidation mechanisms in the form of computational models supported by experimental measurements is essential. An essential component of the proposed work will be education of undergraduate and graduate students in chemistry and mechanical engineering. Also, on-going activities in K-12 education will continue and be expanded through the Research Experience for Teachers (RET) program.